Integrated circuit ("IC") chips contain a variety of miniaturized electronic circuitry and are widely used in conjunction with printed circuit ("PC") boards to provide composite electrical circuits. A typical IC chip or die is located within a ceramic substrate and has a plurality of circuit inputs and outputs that are coupled to electrically conductive contacts or terminals positioned about the perimeter of the substrate or in various patterns across the bottom surface of the substrate such as in land grid arrays ("LGAs"). This assembly is referred to as an IC package or a chip carrier. During operation, the die generates heat which, if unaccounted for, tends to degrade or even destroy active circuit elements in the die. In addition, such heat severely limits the speed and power capabilities of the integrated circuitry.
Heretofore, IC packages have typically been coupled to a mounting side of the PC board by soldering the electrical contacts of the IC package directly to the PC board. Of course, it is somewhat difficult to replace a faulty IC package with this type of connection inasmuch as each of the electrical contacts of the IC package must be desoldered from the circuit board. Alternatively, IC packages have been mounted into sockets or socket cavities particularly sized and shaped for receipt of the IC package. The socket is thereafter coupled to the mounting side of the PC board at a preselected position designated for the IC package. The use of IC sockets in this manner eases installation and replacement of the IC package since a faulty IC package can be replaced without the need for desoldering the faulty IC package and then resoldering the operable IC package at the appropriate location.
Likewise, the use of wadded conductor contacts or "buttons" mounted in insular substrates to form "button boards" is a known type of interface for electronic circuit coupling. They typically provide both direct coupling and physical separation between electronic circuits, which are commonly formed on adjacent circuit boards. Most frequently, these buttons are retentively engaged in corresponding holes in or passing through the nonconducting substrate carrier board. The ends of these buttons are exposed and typically protrude at the respective surface of the insulative carrier board. Such conductive buttons have low resistance when their exposed ends are compressively engaged with surface contact pad areas on the circuit boards.
However, conventional IC socket designs have required an inordinate amount of time in securing the IC package to its complemental socket, and in turn, securing the socket to the PC board. Conventional IC socket designs have typically comprised a plurality of holes located about the periphery of the socket, each of which must be aligned with respective holes in the circuit board and/or any interfacing board. Each of a plurality of bolts are thereafter separately placed within the holes and secured with complemental washers and nuts for fastening the IC socket assembly to the PC board. In addition, these socket designs required a separate retaining spring to be attached to the socket body after the insertion of the IC chip package. These retaining springs required the use of special tools and the springs were attached during the assembly of the PC board. Thus, in order to effect attachment of these socket assemblies to the circuit board, skilled personnel are required to align and manipulate a large number of parts using various tools.
With these arrangements, a back-up board or back-up plate is commonly utilized to provide sufficient strain relief for securing the IC socket to the PC board. The back-up plate is positioned on a side of the PC board opposite the mounting side and the IC socket. Thus, such IC socket arrangements additionally provide an undesirably high profile. This is particularly problematic in designs where efficient use of circuit real estate is important.
Likewise, conventional IC socket designs now offer unacceptable thermal transfer characteristics. For example, one known arrangement for dissipating heat generated by the IC package is the use of a heat sink attached to the top of the IC package. Such arrangements are shown in Spaight U.S. Pat. No. 4,092,697, Sugimoto et al. U.S. Pat. No. 4,803,546, and Werther U.S. Pat. No. 4,750,092. In other arrangements, thermal conducting elements are used to transmit heat to a heat sink which is mounted on the PC board opposite the IC package, as shown, for example in Pitsai U.S. Pat. No. 4,682,269 and IBM Technical Disclosure Bulletin Vol. 13 No. 1, June 1970 at page 58. In yet another example of an arrangement which provides heat dissipation, Bright et al. U.S. Pat. No. 4,716,494 discloses a removable heat sink attached to the upper surface of an IC package. The use of such a heat sink attached to the IC package raises the profile of the overall structure and thus, diminishes the availability of space.
While these structures satisfactorily provide thermal transfer for IC packages which direct thermal flow upward, they are not suitable for use with IC packages which direct thermal flow downward, i.e., toward the PC board or into the socket. In such IC packages, the thermal transfer area and electrical contacts are located on the same surface. These IC packages use a "cavity up" configuration and incorporate a metal slug disposed in a cavity formed in the IC package to dissipate heat from the die. However, in the cavity up configuration, the metal slug is attached to the lower portion of the IC package, i.e., the mounting side of the IC package away from the thermal transfer element. The metal slug conducts heat generated by the die which thereafter must be appropriately dissipated.